1. Field of the Invention
The present invention relates to a laser processing apparatus that irradiates laser beam onto an object and processes the portions thereof where the laser beam is irradiated, and also, relates to a method for manufacturing a liquid jet recording head whereby to provide the resin ceiling plate of the head with the grooves to form liquid paths, holes, and others by use of such laser processing apparatus.
2. Related Background Art
In recent years, it has become possible for a laser processing apparatus to execute a precise processing. Therefore, the apparatus is used for producing liquid jet recording heads and semiconductor substrates, for example.
The description will be made of an example in which a laser apparatus is adopted and used for producing a liquid jet recording head.
The liquid jet recording head, which records (prints) on a recording medium (a recording paper sheet or the like) by discharging recording liquid (ink) from fine discharge ports (orifices) as flying droplets, is provided with a substrate (heater board) having on it a plurality of electrothermal transuding elements and lead electrodes therefor. It is generally practiced that a glass ceiling plate having a recording liquid supplying tube is overlaid on the substrate after a resin nozzle layer (liquid path formation layer) is laminated on the board, which forms liquid paths (nozzles) and a common liquid chamber. However, a resin ceiling member (hereinafter referred to as a resin ceiling plate) has been developed recently and produced by means of an injection molding or the like to integrally form liquid paths and a common liquid chamber, together with a recording liquid supplying tube and others, while omitting the provision of the glass ceiling plate. This ceiling member is then compressed by means of an elastic member so that it is formed together with the substrate. A liquid jet recording head of the kind contributes to reducing the number of assembling parts, and also, to simplifying the assembling processes significantly. Therefore, it is anticipated that the costs of a liquid jet recording apparatus are reduced remarkably when manufactured.
FIG. 3 is a view which shows the principal part of a liquid jet recording head E.sub.0 using a resin ceiling plate. Here, in FIG. 3, the resin ceiling plate is partly broken in its representation.
The liquid jet recording head shown in FIG. 3 is provided with a substrate 1001 having on it a plurality of electrothermal transducing elements 1001a, and a resin ceiling plate 1002 having the liquid paths 1002a positioned on each of the electrothermal transducing elements, and a common liquid chamber 1002b conductively connected with them. The resin ceiling plate 1002 is integrally formed with discharge ports (orifices) 1002c conductively connected with each of the liquid paths 1002a, together with a cylindrical extrusion 1002f having a recording liquid supplying port 1002e, which is open to the common liquid chamber 1002b.
The resin ceiling plate 1002, which is provided with such liquid paths 1002a and common liquid chamber 1002b for its main body, and also, provided additionally with the orifice plate 1002d and the cylindrical extrusion 1002f, is integrally formed by means of an injection molding and others. Then, the resin ceiling plate 1002 is compressed by an elastic member (not shown) onto the substrate 1001 after positioning them so that each of the liquid paths 1002a is placed on each of the electrothermal transducing elements 1001a. Thus, the plate and substrate are coupled together. The substrate 1001 is fixed to a base plate 1004 by use of screws or some other known means, together with a printed-circuit board 1003 having on it a driving circuit that generates electric signals given to each of the electrothermal transducing elements.
In this respect, a method of manufacture has been developed to prepare a blank (a material to form a head) by means of an injection molding, thus providing a main body before the formation of liquid paths 1002a, an orifice plate 1002d before the arrangement of orifices, and some others altogether. Then, by use of excimer laser, the main body of the resin ceiling plate 1002 is grooved to make each of the liquid paths 1002a. Likewise, by use of excimer laser, the orifice plate 1002d is drilled to make each of the orifices 1002c.
In this way, by the combination of an injection molding and a laser processing, it is possible to manufacture resin ceiling plates at lower costs, and promote the further reduction of costs when liquid jet recording heads are manufactured. Here, the laser processing apparatus, which irradiates excimer laser to groove and drill the blank obtained by the injection molding, is generally provided with a light source to generate laser beam; a projection optical system having a lens to project aperture patterns on the blank by use of excimer laser; a split prism arranged on the optical path between the light source and the lens.
In a laser processing apparatus of the kind thus structured, the lens surface of the projection optical system is locally exposed to a high-energy laser beam. Therefore, the surface precision and physical properties of the portion of the lens exposed to such laser beam are easily deteriorated in a short period of time, thus spoiling the optical characteristics of the lens as a whole. This necessitates lens replacements to be made more frequently, leading to the requirement of more labor and time to execute the complicated replacement operation. As a result, the costs of maintenance increase. The laser processing should also be suspended during such lens replacement operation. This inevitably creates a problem that the throughput is significantly reduced. This problem is yet to be solved.